Wrapping apparatus employing stretching film with improved retaining device

ABSTRACT

A wrapping apparatus employing plastic stretching film for items to be wrapped has entry lines and exit lines, which define a horizontal feeding line, in the proximity of a wrapping station (W) provided with a drive ring apt to bring into rotation a reel of the stretching film around the feeding line, and a holding gripper apt to temporarily hold an initial edge of said film in a starting step of the rotation of said reel. A temporary retaining device of said film provided with an elongated hollow member arranged with the longitudinal axis thereof parallel to the feeding line and having an inner side.

FIELD OF THE INVENTION

The present invention relates to a wrapping apparatus of individual items by means of a thin film of stretchable plastic material. Here and in the following mention is always made of individual items, even though each of them may of course consist of a plurality of smaller units (boxes, bags, bottles, . . . ) joined together.

In particular, the invention relates to an apparatus for the wrapping with stretchable plastic film with an improved holding device.

BACKGROUND ART

It is known that packaging of items can be done by wrapping said items with a winding of thin plastic film.

One of the techniques employed is the one which resorts to heat-shrinking plastic material; this solution is relatively expensive, both due to the cost precisely of the thick plastic film, and to the cost of the plant, which uses a shrink oven, and to the energy costs thereof.

An alternative technique is the one which resorts to a thin film of stretchable plastic material; this film over-all represents a lower cost and the apparatus for performing the wrapping does not imply energy consumptions comparable to those of using an oven.

In particular, this last technique is used on machines which wind the items to be packaged with one or more coils of stretchable film, preferably pre-stretched. The winding occurs defining a relative rotation of a reel of plastic film around the item to be wrapped, establishing a relative movement between the reel and the item along a movement axis for determining winding coils distributed on a certain length.

The winding may occur according to a vertical axis (for example in conventional pallet wrappers), along which the load to be wrapped is arranged standing, or according to a horizontal axis, along which the items to be wrapped are caused to move forward. In this last case, each item is fed to the wrapping station along a conveyor belt or a roller conveyor, halted in this station, then it is wound by the film and then caused to continue on the conveyor belt of the wrapping line.

According to the prior art, for performing the winding around an horizontal axis the use of a reel-holding carriage is provided, which is caused to move along a circular line, arranged in the wrapping station according to a plane oriented perpendicularly to the supply line of the items and which horizontally encircles the conveyor belt. In the wrapping station, the item is supported exclusively on overhanging guiding means (typically a shelf and any lateral containment rails) which connect the supply portion of the conveyor belt with a moving-away portion. Thus, upon rotation of said reel-holding carriage, the film which unwinds off the relative reel performs a winding which embraces the item as well as said overhanging guiding means. Once the winding has been completed, the item is pushed towards the moving-away line, causing the coils of stretching film to come off longitudinally from the overhanging guiding means: for such purpose, these guiding means are shaped and structured so as to favor the removal of the wrapped item.

Critical steps of this wrapping process are the initial and final ones, respectively, in which the film must be fastened to the item and then it must be severed to present it again to the subsequent item. For such purpose, it is typically resorted to a retaining and cutting gripper, conventionally arranged below the overhanging guiding means, mounted moving in a longitudinal direction to the rotation axis of the reel-holding carrier.

The rectilinear gripper, with retaining axis arranged horizontally and aligned to the rotation axis of the film reel, has two cooperating jaws apt to retain a film edge and to also perform, in a position slightly downstream of the retaining line, a cut in the film. Operatively, the initial end edge of the film is retained by the gripper—stationary in a fixed position—until the forming of at least part of a first film coil around the item to be wrapped, as the reel is displaced in rotation on the reel-holding carriage. In this movement, the film is partly wound on the item and tends to naturally adhere thereto, abutting in tension on the corners. When the reel-holding carriage arrives at a position preceding the possible interference with the gripper, said gripper is longitudinally shifted to come off from below the carriage, however, retaining with it the initial film end edge. The gripper retains the terminal edge in order not to cause the film to lose tension, which film would otherwise tend to come loose, hence also losing adherence from the item even before the completion of a first consolidation coil. In this process, however, the gripper drags with it the initial end of the film, determining a kind of rope of plastic material which then remains embedded between the first coil and the item to be wrapped. If, on the one hand, this film rope is the result of an essential step for ensuring that the initial end of film is not released prematurely, on the other hand, however, it makes up a lateral appendix of the wrapping, which disturbs the aesthetics and the functionality of the wrapping.

In order to avoid this problem, the Applicant has already proposed to make use of a temporary retaining device, apt to retain, by simple resting, the initial film edge to the item to be wrapped. This device supplements the action of the gripper and allows to disengage the gripper in useful time, without it dragging with it the film, despite maintaining the initial edge adherent to the item for the time necessary to complete at least one coil. This temporary retaining device is in the form of a pressure rod, which rests outside the plastic film, pushing it against the item, so as to retain it in position. The shape of the provisional retaining device is such that it can then be taken off the coils, without leaving trace in the wrapping.

However, the Applicant has detected that this system has margins of improvement. In particular, since the temporary retaining device rests outside the first film coil, it is necessary to provide a complex handling control which brings the device to intercept the area occupied by the item after the reel-holding carriage has wound a portion of plastic film, lest the arising of interferences between the two control members.

This handling control is complex and a possible source of adjustment and control problems. Similar problems, related with handling a temporary retaining device, are affecting similar solutions disclosed in U.S. Pat. No. 4,110,957, WO9929573 and EP1471004, where packaging is performed relying on gripping means cooperating with controlled mechanical retaining devices.

EP0713828 further discloses gripping device relying on suction action to retain an edge of the plastic film far from the item to be packaged. This device is always kept outside the path affected by the plastic film reel and hence is not affected in any manner by the technical problems summarized above, which are specific of a wrapping machine having an horizontal feeding line and a film reel brought in rotation around said line.

SUMMARY OF THE INVENTION

The problem at the basis of the invention is therefore that of proposing an apparatus and a wrapping procedure as above, which allows to achieve an impeccable winding of stretching film, with the smallest complexity possible in the operation of the temporary retaining device.

This problem is solved through the features mentioned in essential terms in the attached main claim. The dependent claims describe preferential features of the invention.

In particular, according to a first aspect of the invention, it is provided a wrapping apparatus employing stretching plastic film for items to be wrapped, comprising entry line and exit line, which define a horizontal feeding line, having an enter path to and an exit path from a wrapping station provided with a drive ring apt to bring in rotation a reel of said stretching film around said horizontal feeding line, and a holding gripper apt to temporarily hold an initial edge of said film in a starting step of the rotation of said reel, wherein it is also provided a temporary retaining device of said film comprising a stationary hollow elongated suction member arranged with a longitudinal axis thereof parallel to said exit path and having an inner longitudinal side located so as to end up just opposite an item to be wrapped during the permanence in the wrapping station, and an outer longitudinal side provided with at least an air suction intake.

According to another aspect, the hollow elongated member has a flattened transversal section and has a single intake in the shape of an elongated slit. Preferably, a net having small mesh is laid on the inner side of said hollow member, covering said slit. The net can have a mesh of 0.2×0.2 mm and the slit a width of 2 mm.

According to a further aspect the elongated hollow member is mounted cantilevered on a small support frame fastened upstream of said drive ring. Preferably, the position of said elongated hollow member, with respect to said feeding line, is adjustable.

Moreover, said elongated hollow member is arranged preferably on the side of the feeding line which is closest to said holding gripper with respect to the movement direction of said reel.

According to a different aspect, it is provided a wrapping method for wrapping items employing stretching plastic film, comprising

moving an item along an horizontal feeding line having entry line and exit line, having an enter path to and an exit path from a wrapping station provided with a drive ring apt to bring in rotation a reel of said stretching film around said horizontal feeding line,

driving a holding gripper to temporarily hold an initial edge of said film in a starting step of the rotation of said reel, and further comprising the following steps providing a temporary retaining device of said film comprising a stationary hollow elongated suction member arranged with a longitudinal axis thereof parallel to said exit path and having an inner longitudinal side located just opposite and brushing the item to be wrapped during the permanence in the wrapping station,

applying vacuum from an air suction intake provided on an outer longitudinal side of said hollow suction member so as to keep said plastic film adjacent to said outer longitudinal side of the hollow member,

releasing said initial edge of film and withdrawing said holding gripper before said reel has completed one single coil of stretching film around said horizontal feeding line.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention are in any case more evident from the following detailed description of a preferred embodiment, given purely as a non-limiting example and illustrated in the attached drawings, wherein:

FIG. 1 is a perspective overall view of an exemplifying winding apparatus provided with a device according to the invention;

FIG. 2 is a detail view of FIG. 1, wherein an embodiment of the invention is shown;

FIG. 3 is a side elevation view of a sucking device according to a preferred embodiment of the invention; and

FIG. 4 is a enlarged view of the detail in the square A of FIG. 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

As schematically illustrated in FIG. 1, a stretching-film wrapping apparatus comprises an entry line 1 a, for example a slide or a roller conveyor along which the items to be wrapped are caused to move forward, a wrapping station W and an exit line 1 b, itself in the form of a slide or roller conveyor.

The items move from entry line 1 a to exit line 1 b, crossing wrapping station W, along a straight line or according to a different path. For example, as illustrated in FIG. 1, the entry line is arranged at 90° with respect to the axis crossing wrapping station W: the items arrive in the proximity of the wrapping station along a sliding plane and then they are pushed crosswise, through station W, by a pushing device S.

The items, in the proximity of the wrapping station, are caused to pass through the supply portion of entry line 1 to a temporary resting shelf 2. This shelf 2 projects in a cantilever manner through the wrapping station and ends at a short distance from the moving-away portion of exit line 1 b (as clearly detectable in FIG. 2). Shelf 2 has indeed the function of supporting the item during the winding with the stretching film and, at the same time, of easing the translation thereof towards the moving-away portion of exit line 1 b despite the application of coils of plastic wrapping film. In its supporting and guiding function, shelf 2 is preferably aided by one or more upper rails 3, which limit laterally the item during the translation and winding thereof with the film. Overall, shelf 2 with rails 3 will be referred to in the following as guiding means.

In wrapping station W a control ring 4 is provided, in a way known per se, rotatably mounted—through a plurality of guiding wheels 4 a fastened to a base frame—on a plane perpendicular to the progress direction of the items. With control ring 4, brought in rotation through a suitable motorization (not shown in detail), a carriage 5 is mounted integral, whereon a shaft 6 is installed supporting a reel of stretchable plastic film and a relative pre-stretch assembly.

Below cantilever shelf 2 a gripper 7 is provided gripping the initial end of film P, which unwinds off the reel. At beginning of operation, gripper 7 performs the double function of retaining the initial edge of film, as well as of severing it when it must be separated from the remaining film wound on the wrapped item. Also at the end of each wrapping cycle, gripper 7 is suitably shifted, according to ways known per se, to grip again the film stretched between the reel and the wrapped item and thus retain the new initial edge of the subsequent wrapping.

In the following no further details on gripper 7 will be provided, since the layout thereof is widely known and, per se, it does not form an object of the present invention.

In order to overcome the prior art drawbacks, according to the invention a temporary retaining device of the plastic film is furthermore provided, regardless of gripper 7, arranged in a position meant to be adjacent at a short distance to a surface of an item when it is in the winding station.

In particular, such a retaining device, according to the invention consists of elongated hollow member 8, preferably flattened, arranged with the longitudinal axis thereof according to the progression axis of the items within wrapping station W. Hollow member 8, shaped as a rod, has an inner side, meant to end up just opposite to the item during the permanence thereof in wrapping station W, and an outer side provided with at least intake means 8 a. In the preferred embodiment, illustrated in FIG. 2, a single intake means is provided in the shape of a slit 8 a elongated in the longitudinal direction of hollow member 8, but it is not ruled out to be able to provide a series of small aligned holes or other. The rectilinear slit has proven the most advantageous one, because it produces a good intake and retaining effect of the film, without causing tearing in the same.

According to a preferred embodiment, the intake means where vacuum is operated through the hollow member 8, are in the shape of a rectilinear slit provided on the inner side with a net having small mesh. In other words, a metallic net having a small mesh is laid on the inner side of the hollow member 8 to cover the slit. With the term “small” it is here meant a mesh having a size smaller then the transversal size of the elongated slit. For example, the net has a mesh of 0.2×0.2 mm and the slit has a width of 2 mm.

In this way, the external side of the hollow member 8 is not affected by the net, but the whole aperture of the slit is partially obstructed by the presence of the net. This arrangement has proven to be excellent to firmly retain the plastic film, but preventing any tear of the film due to the high local stress caused by vacuum through the narrow slit.

FIGS. 3 and 4 disclose a further embodiment where two parallel lines of narrow slit segments are provided, the slit segments belonging to the two lines being staggered each other.

Hollow member 8 is connected at the base thereof to a vacuum intake socket, such as to bring into depression an inner cavity thereof and hence cause an intake flow in correspondence of intake means 8 a.

The crosswise dimension of elongated hollow member 8 is chosen as compromise between the lesser bulk and an acceptable sizing of the inner cavity, in order not to have a high pressure loss on the intake flow, as well as a suitable resistance of the structural walls. Preferably hollow member 8 has a rectangular tubular section, for example of the size 20×10 mm with thickness 1.5 mm.

As clearly shown in FIG. 2, elongated hollow member 8 is mounted cantilevered on a small support frame 9, said frame fastened to the apparatus in the proximity of the base of shelf 2. In substance, the temporary retaining device with intake means is steadily mounted—that is, without handling and/or control during operation of the wrapping station—upstream of the wrapping station and projecting cantilever-like in the area affected by the movement of the spool of plastic film. Preferably, elongated hollow member 8 is installed on the side of the item which is first invested by the plastic film coming from the gripper 7 during the winding movement of the reel. In other words, elongated hollow member 8 is installed on the side which is nearest to holding gripper 7 with respect to the movement path of the reel.

In other words still, in the cycle start step, the reel is always found in a position next to holding gripper 7, typically on one of the two sides (depending on the winding direction) of the item progression line: if this is defined as starting side, elongated hollow member 8 is mounted on this same starting side.

The position of temporary retaining device 8 is stable, the size of items to be wrapped being the same, but can be adjusted differently (moving supporting frame 9 with respect to the frame of the apparatus) between one cycle and the other, upon the varying of the dimensions of the items to be wrapped. As a matter of fact, it is relevant, for the purposes of the inventive teaching, that the inner side of elongated hollow member 8 is found just opposite and brushing against an item during the wrapping, so as to offer the least bulk possible between the item and the film coils which are wound thereon.

As a matter of fact, during the operation the item to be wrapped is pushed into the wrapping station, sliding just before the inner side of hollow suction member 8. The initial edge of film is retained, in a manner known per se, by underlying holding gripper 7. Moving carriage 5 is driven into rotation on ring 4 and begins to arrange a coil of plastic film around the item to be wrapped: the film hence adheres to the lower part of shelf 2, to the item and then it rests on the outer side of hollow member 8; due to the depression obtained along slit 8 a, the film is retained against hollow member 8; in this step it is already possible to release the grip of the initial edge of film, inserted in gripper 7, and cause said gripper to move backwards so as to exit the area effected by the reel movement. In the meantime the reel winding movement continues, which completes the laying of a first film coil around the item, and so on also the subsequent ones.

At the end of the winding, air intake through hollow suction member 8 is interrupted, so that the film is no longer retained on the outer side of the temporary retaining device. The item can thus be pushed forward, on exit line lb, and the film coils will smoothly come off from retaining device 8 and from guiding means 2 and 3—longitudinally aligned with the exit path—which, for the purpose, may be coated with a low-friction material. Due to the minimum crosswise bulk of hollow member 8, the coils of plastic film nevertheless remain sufficiently taut on the wrapped package, taking up part of the elastic stretching.

As can be well understood, with the device according to the invention the objects set forth in the preliminary remarks are perfectly achieved. The gripper must no longer intervene to retain and stretch the initial edge of film, hence the unpleasant plastic rope no longer forms in the wrapping. Moreover, the device of the invention is extremely inexpensive and simple from a construction point of view, because it requires only one air suction line and implies no moving part: thus it may be applied to any winding apparatus, even an already existing one, without having to make significant structural changes.

However, it is understood that the invention must not be considered limited to the special arrangement illustrated above, which represents only an exemplifying embodiment thereof, but that a number of variants are possible, all within the reach of a person skilled in the field, without departing from the scope of protection of the invention, as defined by the following claims. 

What is claimed is:
 1. A wrapping apparatus employing stretching plastic film for items to be wrapped, comprising an entry line (1 a) and an exit line, which define a horizontal feeding line, having an enter path to and an exit path from a wrapping station (W) provided with a drive ring apt to bring in rotation a reel of said stretching film around said horizontal feeding line, and a holding gripper apt to temporarily hold an initial edge of said film in a starting step of the rotation of said reel, further comprising a temporary retaining device of said film including a stationary hollow elongated suction member arranged with a longitudinal axis thereof parallel to said exit path and having an inner longitudinal side located so as to end up just opposite an item to be wrapped during the permanence in the wrapping station (W), and an outer longitudinal side provided with at least an air suction intake.
 2. The apparatus as claimed in claim 1, wherein the hollow elongated member has a flattened transversal section and has a single intake in the shape of an elongated slit.
 3. The apparatus as claimed in claim 2, wherein a net having small mesh is laid on the inner side of the hollow member covering the slit.
 4. The apparatus as claimed in claim 1, wherein the elongated hollow member is mounted cantilevered on a small support frame fastened upstream of said drive ring.
 5. The apparatus as claimed in claim 4, wherein the position of the elongated hollow member, with respect to the feeding line, is adjustable.
 6. The apparatus as claimed in claim 4, wherein the elongated hollow member is arranged on the side of the feeding line which is closest to the holding gripper with respect to the movement direction of the reel.
 7. A wrapping method for wrapping items employing stretching plastic film, comprising: moving an item along an horizontal feeding line having an entry line and an exit line, having an enter path to and an exit path from a wrapping station (W) provided with a drive ring apt to bring in rotation a reel of said stretching film around said horizontal feeding line, driving a holding gripper to temporarily hold an initial edge of said film in a starting step of the rotation of said reel, providing a temporary retaining device of said film including a stationary hollow elongated suction member arranged with a longitudinal axis thereof parallel to said exit path and having an inner longitudinal side located just opposite and brushing the item to be wrapped during the permanence in the wrapping station (W), applying vacuum from an air suction intake provided on an outer longitudinal side of said hollow suction member so as to keep said plastic film adjacent to said outer longitudinal side of the hollow member, and releasing said initial edge of film and withdrawing said holding gripper before said reel has completed one single coil of stretching film around said horizontal feeding line. 